There exists within the art, apparatus and method for coupling reinforcing bars used in structural concrete, such coupling commonly involving the use of a tubular steel coupling body or sleeve configured to receive end portions of the reinforcing bars. Typically, the bars are held in place within the coupling body using a number of engagers, these being for example, bolts or screws which engage into the reinforcing bars thereby wedging the bars against an inner surface of the tubular body providing the couple.
Typical coupling devices found in the art generally comprise engagers having pointed end portions to achieve an engaging into the reinforcing bars and not an engaging onto an outer surface of the bars thereby providing established contact between coupling device and reinforcing bars in an attempt to provide a strong couple. Through the provision of engagers being bolts or screws configured with pointed end portions the coupled reinforcing bars are both wedged firmly against an inner surface of the tubular body in addition to providing resistance to a laterally applied loading force, or tensile force. In particular, EP 0554972, GB 2220241, U.S. Pat. No. 5,046,878, U.S. Pat. No. 5,909,980, U.S. Pat. No. 6,202,282 and U.S. Pat. No. 5,664,902 all disclose a coupling device comprising a plurality of engagers, each engager comprising a pointed or conical end portion configured for bar penetration. A typical coupling device as disclosed within these documents and found in the art is detailed in FIG. 1 herein. FIG. 1 herein illustrates a side elevation view of a bar coupling device 100 as disclosed in the art comprising an elongate tubular body 102, a plurality of engagers 103, at least one gripping surface 104 and an inner surface 105. As is common in the art, coupling device 100 is configured to receive reinforcing bars, in particular their end portions, 101 via elongate tubular body 102. Engagers 103 are then adjustably positioned through tubular body 102 thereby engaging into bars 101 which in turn provides a wedging of reinforcing bars 101 against internal surface 105 at for example a specific gripping surface 104.
An alternative approach for the provision of coupling reinforcing bars is disclosed in GB 2127512. This document discloses a coupling device comprising an elongate tubular body configured to receive bar end portions, the bars being engaged by a plurality of engagers, in the form of bolts configured with flat end portions for engaging onto an outer surface of the bars. A consequence of reduced interaction and contact between the coupling device and reinforcing bars, via the non-penetrating engagers, is a requirement for additional contact between coupling device and reinforcing bar so as to provide an adequate coupling strength. This is provided for in GB 2127512 in the form of a settable material as detailed with reference to FIGS. 1 and 2 therein. The settable material is introduced between the coupling device and the reinforcing bars whereby upon setting, coupling of the reinforcing bars is achieved.
The requirement for a settable material within the coupling device, to be introduced in situ, introduces numerous disadvantages. In particular, settable materials found in the art comprise low fire resistance introducing, in turn, safety concerns. Cementitious grout has been employed to overcome the problem of using low fire resistance material, however this in turn creates additional problems. As a result of the grout having high viscosity, air pockets or voids within the coupling region are observed resulting in a weak joint. The present invention described herein is directed, in general, although not exclusively, to a coupling device being operable without the requirement of a settable material, relying instead on the nature and construction of the coupling device to provide a strong couple. To this type of device we now turn.
With reference to the prior art coupling device of FIG. 1 herein; in response to a laterally applied loading force to the reinforcing bars 101, this loading force is transferred from bars 101 to the coupling device in gradually reducing magnitude from outer most regions 106 progressively through to inner most regions 107. Accordingly, the region of the bars 101 under the greatest stress, following the applied loading force, corresponds to the position of the outer most engager 108 as, in this region, a maximum transfer of loading force from bar 101 to coupling device 100 is observed. The amount of loading force transfer then progressively decreases towards the inner most regions of the coupling device 107, as detailed with reference to FIG. 1 herein.
Accordingly, the inventors have realized various disadvantages associated with prior art coupling devices involving a plurality of engagers configured to engage into the reinforcing bars thereby performing a wedging action. In particular, following a maximum loading force applied to the reinforcing bars 101 it is common to observe bar breakage 109 at a region of the bars 101 having reduced cross-sectional surface area in addition to maximum load transfer from bar to coupling device. Due to the degree of penetration of the engagers into the reinforcing bars, the ability of prior art coupling devices to transfer load from bar to coupler body up to and including the ultimate tensile strength of the reinforcing bars is reduced as a result of the reduced cross-sectional area of the bars at various points along the bars within the coupler body. Commonly, at and including the ultimate tensile strength of the bars, at least one bar breaks in a region within the coupler device therefore providing a weak joint between reinforcing bars. Consequently, the region of coupling of reinforcing bars using coupling devices found in the art, reduces the maximum loading force tolerance of the bars used in structural concrete. The coupling providing a weak point within any reinforced structure as a result of both the reduced cross-sectional area of the bars and a large initial load transfer from bar to coupling device. Moreover, bar breakage within the region of the coupler body even at nominal ultimate tensile strength of the bar is considered by some regulatory authorities as failure of the coupler.
What is required therefore is a coupling device configured for providing a strong couple between reinforcing bars up to and including the ultimate tensile strength of the reinforcing bars.
Accordingly, the inventors strive to provide a coupling device which will not represent a weak point within the reinforced structure providing instead a bar coupled region having an equal or higher loading force tolerance to that found at an uncoupled region along the length of the bars.